navbar bg should be white when shrunk, with green link text.
Main menu at top of the page now takes up 8 columns on the large grid, 10 on the medium and 12 on the small and XS grids and is centered. Added a col-centered class for this, as described in Approach 2 here: http://stackoverflow.com/questions/18153234/center-a-div-using-bootstrap-3-markup-or-css.